Byron Kiourtzoglou

About Byron Kiourtzoglou

Byron is a master software engineer working in the IT and Telecom domains. He is always fascinated by SOA, middleware services and mobile development. Byron is co-founder and Executive Editor at Java Code Geeks.

Generate a File Checksum value in Java

In this tutorial we are going to see how to generate a file’s Checksum value in Java using the SHA-1 hash function. If you are working on your applications security specs it might be useful to consider using checksums to improve the security and integrity of file transfer or file sharing actions.

In short, the basic steps one should take in order to calculate the checksum value of a file are:

  • Create an MessageDigest instance with the SHA-1 function using MessageDigest.getInstance("SHA1") method.
  • Open and read the file using a FileInputStream.
  • Update the MessaDigest with the new bytes you read from the file using MessageDigest.update method
  • Then use a StringBuffer to convert and print the MessageDigest in hex representation.

Let’s take a look at the code:

package com.javacodegeeks.java.core;

import java.io.FileInputStream;
import java.security.MessageDigest;

public class FileCheckSumExample {

	public static void main(String args[]) throws Exception {

		String filepath = "C:\\Users\\nikos7\\Desktop\\output.txt";

		MessageDigest messageDigest = MessageDigest.getInstance("SHA1");
		
		FileInputStream fileInput = new FileInputStream(filepath);
		byte[] dataBytes = new byte[1024];

		int bytesRead = 0;

		while ((bytesRead = fileInput.read(dataBytes)) != -1) {
			messageDigest.update(dataBytes, 0, bytesRead);
		}
		

		byte[] digestBytes = messageDigest.digest();

		StringBuffer sb = new StringBuffer("");
		
		for (int i = 0; i < digestBytes.length; i++) {
			sb.append(Integer.toString((digestBytes[i] & 0xff) + 0x100, 16).substring(1));
		}

		System.out.println("Checksum for the File: " + sb.toString());
		
		fileInput.close();

	}
}

Output

Checksum for the File: 89168dc12b380ab3c84917bc5a8a6c6e9452da1f

 
This was an example on how to generate the checksum value of a File in Java.

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